UPDATE 2-Canadian Oil Sands profit tumbles with oil price

* Q1 EPS falls to C$0.09 vs estimate of C$0.03

* Lower oil prices, operating problems cause drop

* Shares up 5 percent (Adds details)

CALGARY, Alberta, April 29 (Reuters) - Canadian Oil Sands Trust (COS_u.TO), which holds the biggest stake in the world's No. 1 oil sands producer, said Wednesday its quarterly profit dropped 86 percent due to skidding oil prices and difficulties mining enough ore to run processing plants full out.

The trust, which has a 36.7 percent share of the Syncrude Canada Ltd joint venture, said net income fell to C$43 million ($36 million), or 9 Canadian cents a trust unit, from C$298 million, or 62 Canadian cents a unit, in the first quarter of 2008.

The profit beat the average analyst estimate of 3 Canadian cents per unit, as compiled by Reuters Estimates.

Cash from operating activities fell 89 percent to C$50 million, or 10 Canadian cents a unit, from C$441 million, or 92 Canadian cents a unit. Operating costs per barrel rose to C$38.78 from C$35.93.

Syncrude's oil production rose 2.6 percent to 274,000 barrels of synthetic crude a day from 267,000.

Unplanned maintenance and constraints on bitumen supply at the sprawling northern Alberta site held back output in the quarter, Canadian Oil Sands said.